Type 1 Diabetes Mellitus is a multifactorial polygenetic autoimmune disease, where the insulin producing β-cells are selectively destroyed. The initiating events and precise mechanisms leading to selective β-cell destruction remains unknown. One current hypothesis [3] is that in genetically predisposed individuals the β-cells are influenced by factors from the internal or external environment which can damage the β-cells (e.g. cytokines, virus and chemicals) and then lead to release of β-cell specific proteins. During the destructive process IL-1β is released by macrophages in the islets and the cytotoxic effects of IL-1β on the β-cells results in production of free radicals (e.g. nitric oxide (NO.), super oxide (O2.) and hydroxyl (OH−) inside the β-cells. Free radicals and NO. are also produced in and secreted from macrophages in the islet infiltrate. The effects of free radicals are attempted scavenged by β-cell protective proteins (e.g. haeme oxygenases and manganese superoxide dismutase (MnSOD)) [25, 26]. A race between protective and destructive mechanisms is initiated, and when the destructive mechanisms exceed the protective mechanisms, the β-cells die [3].
Autoimmune insulin-dependent diabetes mellitus (T1DM) is caused by specific destruction of the insulin producing β-cells in the islets of Langerhans in the pancreas. During this process islets are infiltrated with macrophages and lymphocytes, releasing a mixture of cytokines, such as interieukin-1β (IL-1β), tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ), which is specifically toxic to the β-cells. Cytokines have been demonstrated to induce free radicals such as nitric oxide (NO.), catalyzed by inducible nitric oxide synthase (INOS) and oxygen derived radical.
Development of Type 1 Diabetes Mellitus (T1DM) is characterized by mononuclear cell infiltration in the islets of Langerhans (insulitis) and selective destruction of the insulin producing β-cells [1, 2]. It is generally accepted that the autoimmune destruction of the β-cells result from interactions between various environmental factors and immune mechanisms in genetically susceptible individuals [3]. The very first events initiating the destructive process has not been described yet. Cytokines, in particular interleukin-1β (IL-1β), are known to be released within the islets in low concentrations by a limited number of nonendocrine cells in sufficient quantities to inhibit and modulate the β-cell function in vitro [4]. In response to low concentrations of IL-1β islets increase insulin release but insulin release is decreased at high concentrations of IL-1β. Furthermore IL-1β influences many important cellular functions such as decreasing DNA synthesis, decreasing protein synthesis and intracellular energy production and induction of apoptosis. Many of these effects are mediated through induction of the inducible NO syntase (INOS) and its product, the free radical nitric oxide (NO.) [5]. The present investigators hypothesize that the β-cell when exposed to IL-1β initiates a self protective response in competition with a series of deleterious events, and that in β-cells the deleterious prevail [3]. In support of this, overexpression of scavengers of free radicals such as catalase and glutatione peroxidase reduces the deleterious effects of cytokines on β-cells [6].
The present investigators have recently described a similar behavior of Wistar Furth (WF) rat islets exposed to IL-1β in vitro [7]. IL-1β induced significant changes in expression level of 105 proteins in WF islets where both protective proteins e.g. such as galectin-3 and HSP70 are up-regulated and deleterious protein changes e.g. mortalin and lamin A and B1, were identified. In addition proteins involved in mitochondrial energy production were suppressed e.g. adenylate kinase and mitochondrial ATP synthase regulatory subunit B [7].
The BioBreeding diabetes prone (BB-DP) rat spontaneously develops a diabetic syndrome with many characteristics common with human T1DM [8]. Originally the BB-DP rat strain has been breed from a WF rat colony [9]. Strain-dependent variations in β-cell sensitivity to IL-1β effects have been demonstrated in vitro and in vivo [10] [11]. Islets isolated from grown Norway rats were less sensitive to IL-1β compared to Wistar Furth (WF), Lewis-Scripps (LS) and BB (both diabetes prone (DP) and diabetes resistant (DR)) rats. The BB-DP rat islets produce lower protective stress responses (HSP70) than the diabetes resistant BB rat which might promote enhanced vulnerability and β-cell destruction [12]. The present investigators have previously shown that there is no difference in nitric oxide (NO.) production and 24 hour accumulated insulin release in BB-DP and WF islets in response to exposure to 150 pg/ml IL-1β for 24 hours [13]. The higher resistance to IL-1β induced inhibition of β-cell function in vitro and in vivo in BN rat islets was associated with lower expression of inducible nitric oxide synthase (INOS) compared to Wistar Kyoto and Ls rats [11].
The present investigators previously demonstrated that IL-1β induces reproducible and statistically significant changes in the expression level of 82 protein spots in BB-DP rat islets of Langerhans in vitro out of a total of 1.815 protein spots visualized by 2 dimensional gel electrophoresis. Twenty-two protein spots were up-regulated and 60 protein spots down-regulated [13].
Recently, the present investigators have separated approximately 1.900 protein spots according to molecular weight and isoelectric point (pI) by high resolution 2 dimensional gel electrophoresis of WF rat islets of Langerhans [14]. One hundred and five of these protein spots changed expression levels after IL-1β incubation in vitro and the majority of these proteins have now been identified by mass spectrometry. The identified proteins were classified into the following functional groups (in brackets number of different proteins): a) energy transduction and redox potentials (n=14), b) glycolytic enzymes (n=10), c) protein synthesis (n=5), d) chaperones, protein folding and translocation (n=19), e) signal transduction, regulation, differentiation and apoptosis (n=9) suggesting broad variety of pathways involved in IL-1β toxicity on islets [7].